This invention relates to apparatus for repairing or cutting a seat for a metal seal in a conduit or tool member in an earth well and metal seal apparatus for installation in the well to seal on the seat.
There have been a number of failures of conventional seal rings made of elastomeric materials, which were used to seal in bores in downhole well tools, anchored in well casing. These seal rings are usually mounted on a seal unit connected to the lower end of a flow conduit lowered into the well and into a tubular seal receptacle on top of downhole well tools, such as liner hangers or production packers, which has been smooth bored inside for sealing. Examples of such use of elastomeric seals is shown on page 1456 of the 1982-83 "Composite Catalog of Oilfield Equipment and Services", in the form of o-ring and compression seals on "tie-back" stems and packers.
A sealing system utilizing elastomeric and metal seal rings is disclosed in U.S. Pat. No. 4,288,082, of which I am the inventor. Another example of a sealing system utilizing metal, elastomeric and thermoplastic materials, is disclosed in U.S. Pat. No. 4,433,847 to Weinberg.
The apparatus and method of this invention provide a unique milling tool for cutting and/or finishing a seat on a shoulder in a well conduit or tool anchored in the well casing. A seal unit, having a deformable metal seal ring slidably mounted near an outside seal surface on its lower end, is then lowered on pipe into the well until an outside seal surface on the ring engages the seat. Weight of the pipe lowering string is then applied to the seal unit, which compresses the metal ring between the seat and seal unit and deforms the metal seal ring sufficiently to seal on the seat and seal unit and establish the seal between the seal unit and well tool. The metal seal of this invention will better resist high deep well temperatures and chemical deterioration of elastomeric materials caused by hydrocarbons in earth wells and provides a much longer lasting and more reliable seal than elastomeric material seals previously used. Higher pressures can be sealed because much greater compressive loads can be placed on the metal seals than on elastomeric materials.
The milling tool of this invention provides for formation of a seat on a shoulder in a well conduit while in the well. This milling tool will cut and smooth finish the whole seat or "redress" or smooth finish for sealing a seat previously cut. The downward force of the milling tool cutter on the seat may be controlled. The profile formed by the milling tool mates with the outside seal surface on the metal ring and the outside seal surface on the lower end of the seal unit. The seal unit metal ring is thicker, in the section compressed between the seat and the seal unit, and prevents the outside seal surface on the lower end of the seal unit from initially engaging the seat. When sufficient load is placed on the seal unit to compress the metal ring between the seal unit and seat and reduce the thickness of the metal ring, the outer seal surface on the lower end of the seal unit also engages the seat and forms an additional metal to metal seal with the seat prepared by the milling tool. The additional seals' diameter of seal is smaller than the seal rings' diameter of seal and the additional seal exposes a smaller sealed area reducing the "piston" force trying to move seal unit up. Additionally, the smaller sealed area on the additional seal provides for the sealing greater pressures with the same load down on the seal unit. Further, the additional area engaged in compression provides for the support of greater pipe loads on the seal unit and prevents the slidable metal ring from being crushed so it will no longer seal.
Downwardly and inwardly tapering angles of 5.degree. to 45.degree. with the longitudinal axis of the tools were found useful for all metal seal surfaces. Angles of 12.degree.-15.degree. were found preferable for metal seal surfaces and cutting on seats with the milling tool.
The system of this invention is particularly useful to replace failed elastomeric downhole well seals with longer lasting metal seals and reseal between well tool members allowing the well to continue production.
An object of this invention is to provide apparatus and a method for establishing an improved seal between conduit joints in a well.
An object of this invention is to provide apparatus for cutting and/or finishing a seat having a particular profile on a shoulder in a well conduit.
Another object of this invention is to establish an improved seal between conduit joints by retrieving only a portion of the conduit string from the well.